Match mesh on top of another
My suggestion is to use the Shrinkwrap modifier. Just add it to the costume object and set the model mesh as the target object. Enable Keep Above Surface and adjust the offset value, so your costume mesh will stay above the model mesh.



With the Shrinkwrap modifier your costume mesh will follow the exact shape of the target mesh, so the mesh will be modified. But if you just want to completely cover the model without changing the costume mesh, use the Displace modifier - tweak the Strength value.